The Co/CoNi sequential configurations based on transparent basalt substrates toward excellent microwave absorption

The typical design for electromagnetic wave absorbing materials is the composites made of high dielectric components and magnetic materials, which is a single type. This article presents a unique paradigm for high microwave absorption (MA), whereby the transparent basalt substrates are evenly covered by the sequential configurations formed by the entangled Co/CoNi nano-units. The sequential nanostructure consistently displays a net-like morphology at a 5/10 min reaction for the higher Co content in CoNi, exhibiting the regular variety for complex permittivity. On the other hand, it is constructed by the spherical nano-units with a higher Ni ratio in CoNi. After 5 min of reaction, the nanospheres are arranged with the nanogaps, or they are continuously arranged on basalt after 10 min. Correspondingly, the basalt/CoNi composites exhibit unfavorable 'mutation' characteristics with the too-small or too-large complex permittivity, detrimental for optimized MA. As expected, with the specific Co/Ni ratio, the net-like basalt/CoNi obtained at 5 min displays outstanding MA due to appropriate dielectric loss and strong magnetic coupling (-61.98 dB at 2.03 mm, 4.665 GHz at only 1.47 mm). Especially, the nano-scale magnetic coupling is confirmed by micromagnetic simulation. This work breaks the limitations of traditional absorbers and provides new design ideas about magnetic-dielectric components.